Process of making cellulose nitrate sheeting including imbibition



Aug. 13, 1935. E. K. CARVER ET AL PROCESS OF MAKING CELLULOSE NITRATE SHEETI NG INCLUDlNG IMBIBITION Filed May 26, 1955 AIR OUTLET HOT AIR INLET MiHmzmMUmmliAMyud,

Patented" Aug. 13, 1935 "PROCESS OF MAKING CELLULOSE NITRATE SHEETING INCLUDING IMBIBITION I Emmett K. Carver and Clarence L. A. Wynd, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New York Application May 26, 1933, Serial No. 673,036 .13 Claims. (01. 1s '57) p I This inventionrelates to cellulose nitrate sheeting and to a method of producing it. More particularly it relates to a method of preparing cellulose nitrate sheeting from asolution of nitro- 5 cellulose in solvent liquid in which acetone, predominates by casting the sheet upon a suitable surface andthen treating the sheet, after it has set but while still containing considerable acetone, with a liquid in which methyl alcohol predominates, and further drying the sheet.

In the manufacture of cellulose nitrate sheeting, such as'in the production of cellulose nitrate film base ranging from .005. to,.0l0 of an inch in thickness, and of any suitable width, the nitrocellulose is dissolved in a suitable solvent to make what is termed in the trade a dope of about the consistency of honey. This dope is permitted to flow upon a large wheel, such as a driven cast iron wheel having a smooth nickel or chromium 2g plated". surface, which wheel rotates in a casing through which air is circulated, permitting the solvent to evaporate from .the dope and harden into a sheet of sufficient toughness to strip from the wheel beforeiit has made a complete revolution, whereupon the sheet is led through curing chambers over idle rolls and curing drums main- ,tained at a suitable temperature (and through which. air is circulated) and then wound upon a shaft forstorage or further use, such as coating with emulsion to form photographic film.

We have noted the "rather striking fact that while sheeting may be produced more rapidly from a dope in which acetone predominates as asolvent than from a dope in which-methyl alcohol predominates as the 'solventliquid, nevertheless a film having better wearing properties, higher tensile strength and much higher flexibility results from sheeting produced from the methyl alcohol dope.

40 We have discovered a method of producing cellulose nitrate sheeting wherein the speed of coat .ing from an acetone dope is utilized and yet the unusual micelle structure which gives the sheeting the higher wear and tear resistance, higher ten- .sile strength and greater flexibility is obtained.

'Accordinglyjit'is an object of ouriinvention to provide a process for preparing nitrocellulose sheeting which will have the speed of coating obtained with acetone dopes and the physical structure of sheeting produced from methyl alcohol dopes. Other objects will be apparent from a further perusal of this specification.

. Inits broader aspects,- our invention comprises preparing a suitable dopeby dissolving cellulose nitrate in a solvent liquid in which acetone predominates (at least in its effect upon micelle structure), casting or'coating this dope into the form of a sheet permitting suflicient acetone to evaporate from the sheet to permit stripping of the sheet from the casting or coating surface, 5

then treating the sheet with a liquid in which methyl alcohol predominatesand permitting further volatile liquid to evaporate from the sheet.

Our process is not to be confused withvthose involvingthe application to the sheeting (before 0 it is stripped from the casting or coating surface and while it still contains a large proportion of solvent) of certain treating solutions, such as a solvent or solvent mixture, to prevent or modify. I curling tendencies of the sheeting, or of certain l5 treating solutions, such as dyes, coatings and the like, to the sheeting while it is still on the casting surface for alteringthe color, moisture resistance, static properties, etc. of the sheeting. Noris our process to be confused with that'type of process wherein the sheeting, after it leaves the coating surface and passes through the curing chambers .and as a substantially finished or cured sheet is treated with certain treating baths for removing a small percentage of residual solvent or other 5 constituents of the dope :used in forming the sheeting, this latter being done usually" with an aqueous bath and in all events without scarcely softening thesheet and in no-case being accompanied by a micelle, rearrangement. The effective part of our process acts upon the film preferably at a point in between these two above mentioned types of treatments-and, as will be apparent hereinafter, has an entirely different effect upon the sheeting, although, with less salient jefiect and 35 economy and more difficult handling, our processv is applicable to the treatment of substantially fully cured sheeting. I s A The type of cellulose nitrate whichwe employ is that ordinarily employed, in the manufacture 540 of cellulose nitrate sheeting, namely, nitrocellulose having a nitrogen content of from approximately 1l.5% to about 12.2%. In convert- ,ing thlsnitrocellulose into .a so-called acetone dope, it is customary to employ a solvent liquid .45

containing from 51 to of acetone mixed with from 49% to 0% of methyl alcohol, both the acetone and methyl alcohol being the average commercial grade of substances obtainable upon the market. Highboilers, such as butyl alcohol, 5() and plasticizers, such as camphor, may, of course, be added to the dope as already known. The speed with which it is possible to successfully coat the acetone dope. depends, of course, upon the proportion of acetone contained in the dope gt solution to the sheet. V

:Referring now to thedrawing accompanying this specification and forming .a part-hereof and spreading; etc. It also has probably the highest evaporative rate, since it is a constant boiling mixture with a boiling point very slightly lower than pure acetone. I However, it will be understood that the'micelle arrangement which occurs when a pure acetone dope of nitrocellulose is cast into the form of a sheet and evaporated, Prev-ails. with all nitrocellulose of the sheeting i'type (11.5 to 12.2% nitrogen) down to an acetone content of as low as for the solvent liquid, even though the remainder be methyl alcohol- With nitrocellulose in the lower range of nitrogen content, for instance of from 11.5% to about 12% nitrogen, this acetone effect or micelle'arrangemnt'pre v'ails when a solvent liquid of even a little less than 30% acetone is used. In thisspe'cification, therefore, when we refer in its broader sense to a dop'e' inwhich acetonepredominates, we refer to a dope in which the acetone effect upon inicelle structure predominates. The efiect of acetone upon micelle structure in the sheet may be recog'nized not only by the lower tensile strength, wear and tear; and fiexibility of the' sheet but y itscharatei of tear; Where acetone asserts its predominance one will obtaina rather straight tear, whereas a sheet in whichmethyl alcohol asserts its predominance will give a bevelled tear.

1 The nitrocellulose may be added to the acetonern'ethyl alcoholsolventliquid inthe proportion of one part of nitrocellulose to about five parts of solvent liquid, although frequently anywhere from four to six parts of solvent liquids are employed.

' In thedr'awing -we' have'illustrated several of the preferred embodiments of our invention in I which:

Figure 1 is a diagrammaticsectional elevation of one'jforni of apparatus for. carrying out our imblbition process, and illustratinga convenient method offorming a cellulosenitratesheet, causing it to'imbibea treating solution and subsequently dryingthe treated sheet.

Figure 2 is a sectional elevation of a modified form of the device for applying the imbibition in which like reference numerals refer to like parts, Fig.1 is a diagrammatic side elevation of a suitable appara'tusfor carrying out our invention. In this-apparatus the dope is fed to H the hopper l which is provided .with'an adjust- *able blade or knife 2'for'regulating the thickness 'ofthe coating. This coating is thus deposited upon the surface of a large driven wheel 3 of suitable diameter and width, which is'mounteduponstandards l; As'this wheel 3 rotates slowly in the direction indicated: .by'the arrow, heated air is admitted through the line 5 into the casing ljaswell as through the" line 6, into another portion of thela'pparatus. The air adinitted through line 5 passes in the direction of the arrows around the wheel 31 within the casing T, theline and casing bothbeing suitably insulated as desired. That part of the air which passesarou'nd the major periphery of the wheel is withdrawn-laden with solvent, at the air outlet -8 while the remainder travels up through the casi'nglilr The 'wheel tis rotated-at a speed which, with the amount of air being circulated I and the amount of dope being used, will permit sufficient hardening of the dope to allow the sheet to be stripped from the wheel at the point p where the roll 9 is placed. A rotational speed of from 5 to .8 revolutions per hour fora'wh'eel having a diameter of 18 1:020 feet, namely a peripheral speedfof about300-'0 feet per hour,

with a plentiful circulation of airv at an inlet temperature of approximately 175-2Q0" F., has

been found satisfactory.

While this sheeting might be conducted through.

the curing apparatus. and sheeting satisfactory for some purposes be thus obtained, it is desirable for use as photographic film base, particularly motion picture film base, that the sheeting have a higher wear and tear resistance and greater flexiparticular importance, the evidence points to the fact that sheeting produced from a methyl alcohol cope havocdifferent micelle structure,

namely, a difierent mannerhywnlch the nitrosheeting produced from an; acetone dope;v We

' havemade the very valuable discovery that sh'eting produced from-an acetone dope; even though hardened sufliciently to permit h'andling thereof,

- bility; While'thedretical considerations are of no 'cellulosemolecules are fitted together than has f This is accomplished by conducting thenitrocellulose sheet over a set 0: rolls I'Oandcver sub-' mersion roll II, which latter .rcll submergesthe nitrocellulose sheet into an imblbition solution, contained in submersion hc'pper lz. From this hopper, the nitrocellulose sheet passes overthe rolls l3 and under submersion roll 14,- sothat the sheeting is submerged in;the imblbition solution contained in the immersion hopper ll. From roll steam or-waterheatedcurlng drums ll,'which are preferably driven, and thenc'e'to wind up HI. For convenience, we have illustrated acasing IS in which the'rolls' l0, l3 and Ware contained and a casingzrin which the curing drums H are com .tained, These two casings arefseparatedby-a bafile122c which leaves an opening adjacent the lower roll I6, throughwhich' the film enters into casing 2| and which permitsv any desired communication'hetwieenth'e casings, "and 2 l A door 2-3. is providedfor removing the sheeting as it is wound upat-l8. Heated air for curing the sheeting. is supplied to the casing 2i through the line 6,,as previously adverted to.- Solventladen air is removed from the casings l9 and. by

means of the air outlet 24 whichconducts the 'sol'vent-ladenairialon'g with air from the outlet 8) to the solvent recovery apparatus, which -re-' movesthe solvent from the air andreturns it to While --we have illustrated the nitrocellulose sheeting as being subjected to imbibition upon both sides of the sheeting andthe most complete conversionof'themicelle structureof the sheeting from the acetone dope type to the inetllyl alcohol either-of the-hoppers l! or It, if a IQss'complete dope type is therebyobtained, wemay subject the sheeting to only asi'ngle immersion, such as in 4'0 i l, the sheet passes"over-rdlls' l64ahd thenceto.

change of the micelle structure is desired. Possibly the most complete change of micelle structension of the sheeting must be more carefully regulated, in order not to pull the sheet in two.

The imbibition solution employed in the hoppers [2,1 and 26 is one composed of a preponderance of methyl alcohol. Considerable latitude is permitted in compounding the imbibition solution, the factors which limit the constituents of the imbibition solution. being (1) methyl alcohol must predominate (2) non-solvents must not be employed in such'proportion as to substantially negative the action of the methyl alcohol upon the nitrocellulose sheeting (3) solvents must not be presentin such proportion as to so drastically attack the nitrocellulose sheeting that it will become so soft as to be pulled apart by the tension required to pull the film over the idler rolls [0, l3 and i6 and the curing drums i1, (4) the time that the sheeting is immersed in'the imbibition solution must be so regulated as to give the desired length of treatment-to the sheeting but not to unduly soften the sheeting and (6) acetone must not be present in sufficient amount to control the micelle structure formed instead of having it controlled by the methyl alcohol, as pointed out in the early part of this specification. :Provided the nitrocellulose employed in pro- "ducing the sheeting. is not too readily soluble in methyl alcohol, we may employ 190% methyl alcohol as the imbibition solution. More preferable, however, is methyl alcohol containing from 1 to 5% of water. Inasmuch as ethyl alcohol has only slight solvent action upon nitro cellulose of this type, we have found it satisfactory to employ as high as 30% ethyl alcohol with as low as about 70% methyl alcohol to form a suitable imbibition solution. Either of these solutions will tolerate a small percentage of solvent, such as acetone, and as a matter of fact, it will be'apparent that some acetone will be taken up by the imbibition solution as the sheeting-still containing a fairly high percentage of acetone-passes through the imbibition solution. We prevent the acetone from accumulating to an extent which would unduly soften the sh'eeting or prevent the micelle rearrangement desired, by regulating the flow of imbibition solution through the immersion hopper at such a speed that the acetone does not accumulate to a detrimental proportion. With for instance three seconds immersion of the sheeting. in the'imbibition'solution, we have found that the acetone content of any of the above imbibition solutions, when used for treating a skin made from a nitrocellulose whose nitrogen content is about l2%, should not be permitted to increase beyond approximately 1.0%. With nitrocellulose of lower nitrogen content, the acetone to be tolerated would be slightly less than 1%. a

The time of immersion of the sheeting in the imbibition solution'is regulated by the speed of the sheeting as it passes through the apparatus and by the depth of immersion of the sheeting in the imbibition solution. We have found that from 1 to 3 seconds immersion time in each, or either,

of the hoppers l2 and I5 is satisfactory, or that 1 to 2 seconds immersion in-the imbibition solution contained in the hopper zfimay be employed.

The air temperature inthe cabinet I!!! will, of course, be somewhat less than that at which it enters the casing 7. It is preferable to regulate film. Also the temperature of the curing drums ll may be increased in the direction of the travel of the film, such for instance as a temperature of 175 F. for the first drum and 225 F. for the tenth drum, with the temperature thereafter being tapered ofi to 175 F. at the fifteenthdrum. Also the drums may be in a vertical'stack as shown, or they may be horizontal or in the shape of an upright orinverted .U', for instance.

While we have illustrated the point of imbibition of the sheeting at approximately the central position of the air-drying section E9 in which the film passes over .a series of rolls, it will be understood that it is intended only that the imbibition take place, in the preferred embodiment of our been stripped'from the casting surface.

As explained above, the entire imbibition may take place at the hopper l2 or at'th-e hopper I5 by immersion in either of these hoppers of a single side of the sheeting, or the hopper 12 may.

be replaced by a hopper 26 of the type shown in Fig. 2, and the hopper l5 dispensed with, or the hopper 15 may be so replaced and the hopper l2 dispensed with. Furthermore, as pointed out above, there may be any number of the rolls 1!), l3 and [6 as may be foundnecessary for the particular result desired. In other" words, the sheeting may be given more or less air-curingprior 'to its imbibition, between the two imbibitions, or

following the single or last imbibition, depending, of course, upon how Well cured the sheeting may be when stripped from the wheel or What temperatures are employed in the air-curing cabinet [9.

Suffice it to say that, preferably we imbibe the sheet with our imbibition solution while the sheet contains a relatively'high percentage of acetone and is thus readily susceptible to an exchange in the nitrocellulose sheet of methyl alcohol for extending it. While there is no limiting point at which the sheet may be subjected to imbibition we would state that it is less desirable to subacetone. Comparatively speaking, we have found 0 stantially completely. cure the sheet before sub- .jecting it to imbibition as the micelle structure of the nitrocellulose has then become rather firmly fixed. Such long immersionmay also be accompanied by undue-softening of the surface of the sheet before penetration of the imbibition solution into the center of thesheet can take place and thus cause difficulties in the handlingof a principlesof our invention.

long strip of sheeting. However, it is to be understood that our process may be employed with substantially fully cured nitrocellulose sheeting even after it has been instorage. Particularly is this true of small sheets which can be handled. by suspending them in the imbibition solution from clips or where a machine especially designed for handling soft sheets is available.

' In this same connection, while we have shown an apparatus for continuously producing sheeting in accordance withour invention, it will be quite apparent that it may be carried out inbatch form, such as by coating the acetone dope upon plates, permitting. the solvent to evaporate from the sheet, stripping it therefrom substantially as soon as itis susceptible of stripping and handling, or even after it has more thoroughly cured, and then imbibing the sheet merely by dropping it into an imbibition solution. This hand operation will, of'course, not be very practical commercially (because expensive) but illustrates the As a guide to those skilled in the art, we would state that from our experience with the process we find that a nitrocellulose sheet may be stripped from its coating surface at a time when it still has remaining therein roughly -15% of acetone (or solvent liquid) and that it'should preferably be imbibed with our methyl alcohol solution any time from thatpoint up to a point in the subsequent curing of the sheet'at which, it still contains' roughly 2% acetone, although as above pointed out, a more thoroughly cured sheet may successfully be subjected to imbibition. percentages of acetone are given not as a limiting factor to our invention, but merely as a guide to those skilled in the art so as to teach them the principles of ourinventionQ Motion picture film having a, base of nitrocellulose' sheeting produced according to our process will be found to endure the wear and'tear of the ordinary cine projection machine for as much as ten'to 100 percent longer than sheeting produced from an acetone dope without being imbibed in. accordance with our invention, the degree of improvement depending on the degree of imbibition obtained. The sheeting of our invention, furthermore, has been found to possess con- ;siderably more flexibility than the flexibility which the acetone dope type of sheeting possesses, for instance. as muchas to more flexibility. The imbibed sheeting also possesses a higher tensile strength. r p Accordingly, it will be observed that we have provided a process which permits the high speed of coating accompanying the use of an acetone dope but having the desirably high wear and tear resistance, increased tensile strength, and increased flexibility of the methyl alcohol dopes which, though desirable to produce, are of such slow coating speeds as to increase the expense of production to a point substantially prohibiting their competition with other types of sheeting.

What We claim as our invention and desire to be'secured by Letters Patent of the UnitedStates is:

'1. The process of preparing nitrocellulose sheeting which comprises casting a dope of nitrocellulose dissolved in a liquid in which acetone predominates in its effect upon the micelle structure of the sheeting, evaporating suflicient solvent therefrom to permit stripping of the sheet, stripping the sheet and treating at least one surface hol predominates.

. of the sheet with a solution in which methyl alco- These 2., The process of preparing nitrocellulose sheeting which comprises casting a dope of nitrocellulose dissolved in a liquidin which acetone predominates in its effect upon the micelle structure of the sheeting, evaporating sufficient solvent therefrom to permit stripping of the sheet,.stripping the sheet and submerging at least one surface of. the sheet in a solutionin which methyl alcohol predominates. p

3. The process of preparing nitrocellulose sheeting which comprises casting a dope of nitrocellulose dissolved in a liquid in which acetone predominates in its effect upon the micelle structure ofthe sheeting, evaporatingsuflicient solvent therefrom to permit stripping of the sheet, stripping the sheet and submerging the sheet for a time in a solutionin which methyl alcohol predominates.

4. The process vof preparing nitrocellulose sheeting which comprises casting a dopeof nitrocellulose dissolved in a liquid in which acetone predominates in its effect upon the micelle structure of the sheeting, evaporatingsuiilcient solvent therefrom to permit stripping of the sheet, stripping the sheet and submerging the sheet in sub stantially pure methyl alcohol.

5. The process of preparing nitrocellulose sheeting whichcomprises'casting a dope of nitrocellulose dissolved in a liquid in which acetone predominates in its effect upon the micelle structure of the sheeting, evaporating suflicient solvent therefrom to permit stripping of the sheet, strip-,

ping the sheet and submer'ging at least one sur face of the sheet with an imbibition solution containing more than 95% methyl alcohol and the remainder substantially water.

6. The I process. of preparing nitrocellulose sheeting which comprises casting a dope of nitrocellulose dissolved in a liquid in which acetone predominates in its effect upon themicelle structure of thesheeting, evaporating suflicient solvent therefrom to permit stripping of the sheet, stripping the sheet and submerging at least one surface of the sheet with an imbibition solution containing more than 95% methyl alcohol, less than 1% acetone and the remainder substantially water.

'7. The process of preparing "nitrocellulose sheeting which comprises casting a dope of nitrocellulose dissolved'in a liquid in which, acetone predominates in its efiect upon the micelle structure of the sheeting, evaporating sufficient solvent therefrom to permit stripping of the sheet, stripping the sheet and submerging at least one surliquid in which methyl alchol predominates and drying the sheet. I

10. The process which comprises submerging nitrocellulose sheeting which has been prepared from a dope in which acetonepredominates in its influence upon the micelle structure in a liquid consisting of substantially pure methyl alcohol.

11. The process which comprises submerging nitrocellulose sheeting which has been prepared from a dope in which acetone predominates in its influence upon the micellestructure in a liquid consisting of more than 95% methyl alcohol and the remainder substantially water.

12. The process which comprises submerging nitrocellulose sheeting which has been prepared from a dope in which acetone predominates in its influence upon the micelle structure in a liquid 10 consisting of more than 95% methyl alcohol, less than 1 acetone and the remainder substantially Water. v

13. The process which comprises submerging nitrocellulose sheeting which has been prepared from a dope in which acetone predominates in,

its influence upon the micelle structure in a liquid consisting of approximately 70% methyl alcohol and about 30% ethyl alcohol.

EMMETT K. CARVER. CLARENCE L. A. WYND. 

